Method of fabricating pressed components

ABSTRACT

A simpler and less expensive method of fabricating pressed components from sheet steel that can be heat treated while inside the press, whereby the material is heated to above its transformation point Ac 3 , pressed, and cooled, controlled, to below its crystalline-transformation point. The sheet is unwound from a coil ( 1 ), heated to above its transformation point, pressed in a press, and separated.

[0001] The present invention concerns a method of fabricating pressedcomponents from steel sheet that can be heat treated while inside apress as recited in Claim 1 herein.

[0002] Components, especially components for the automotive industry,are increasingly being fabricated of sheet steel or steel structuralsection pressed and hardened in the press itself.

[0003] These steels may for example be composed of

[0004] carbon (C) 0.19-0.25

[0005] silicon (Si) 9.15-0.50

[0006] manganese (Mn) 1.10-1.40

[0007] titanium (Ti) 0.020-0.050

[0008] boron (B) 0.002-0.005

[0009] aluminum (Al) 0.02-0.06

[0010] phosphate [sic! scil. phosphorus] (P)<0.025

[0011] sulfur (S)<0.015

[0012] chromium (Cr)<0.35

[0013] molybdenum (Mo) 0.35

[0014] the remainder constituting iron (Fe), including contaminationfrom smelting.

[0015] European Patent 1 300 476 A6 discloses fabricating suchcomponents from plates and structural section. There is, however, adrawback to this method. The plates and section must be heated to atleast 750° C. in a continuous furnace before they can be inserted in thepress. The process is accordingly complex and the equipment complicated.

[0016] The object of the present invention is accordingly a simplermethod of fabricating pressed components from steel that can be heattreated while inside the press, while employing less complicatedequipment.

[0017] This object is attained in accordance with the present inventionin a method of the aforesaid genus by the characteristics recited inClaim 1. Claims 2 through 12 address practical alternative and advancedembodiments.

[0018] The present invention features several advantages. First, inspite of the lower investment in equipment, the fabrication process canbe considerably accelerated. Again, the method in accordance with thepresent invention is extremely flexible, allowing the fabrication ofdifferent shapes from the same coil with no need to readjust the wholefurnace and all the conveying equipment as in the conventional approachusing plates of various dimensions to obtain different-sized components.Furthermore, the equipment can be adapted later to handle uncoatedsheet, the material being subjected to an inert atmosphere while in thepress. Finally, the sheet can be cut while still hot, savingconsiderable wear on the cutter.

[0019] One embodiment of the present invention will now be specified byway of example with reference to the accompanying drawing, a singleFIGURE.

[0020] A strip 1 of steel sheet has been wound into a coil on anunillustrated stand. Strip 1 is unwound from the coil as needed andstraightened if necessary. The unwound and if necessary straightenedstrip is heated in a furnace 2 to a temperature above the material'stransformation point Ac₃. Furnace 2 can be a transverse-field inductionfurnace for example, although a conventional gas-or-electrically heatedfurnace can be employed as an alternative. Downstream of furnace 2 is aholding section 3, where the strip is maintained at a temperature to beemployed for further processing, e.g. above 850° C.

[0021] The holding section 3 in the illustrated example accommodates anunillustrated plane-traveling metal-cutting laser employed to produce aU-shaped cut 5 in plate 4. As will be evident from the schematicillustration, the cut is executed by a series of several parallel laserheads. Plate 4 is maintained fixed at one margin 6, and no manipulatingmechanisms will be necessary to forward it into the downstreammultiple-stage press 7. How plate 4 is fixed at the margin will bedetermined by one of skill in the art in accordance with the specificsituation.

[0022] Other types of metal-cutting tools—saws or punches forexample—can of course also be employed instead of a laser. A plate canalternatively be cut off the strip, in which event, however, a conveyingmechanism will be needed to forward the hot plates to the differentsections of multiple-stage press 7.

[0023] The schematically depicted component 8 in the present embodimentis a reinforcement of the type employed in the doors of motor vehiclesto minimize damage in the event of lateral collision.

[0024] In the first processing section 9 of multiple-stage press 7,plate 4 is pressed into its intended shape and cooled in anunillustrated refrigerated press to below its crystalline transformationpoint, preferably in the present example to 450° C. The press isrefrigerated with water and cools component 8 indirectly.

[0025] The component 8 in the illustrated embodiment is now cooled toapproximately 50° C. in the second processing section 10 ofmultiple-stage press 7. This second cooling stage can be regulated orunregulated. The advantage of such multiple-stage cooling is that thetiming can be distributed throughout the process, cutting the totalfabrication time almost in half. The component can also be cooled insecond processing section 10 by way of the refrigerated press, althoughit can also be cooled directly by air or by another coolant.

[0026] Component 8 is now, in a third processing section 11, completelyseparated from the plate at margin 6. The component can simultaneouslyor subsequently be bored or machined as necessary.

List of Parts

[0027]1. strip

[0028]2. furnace

[0029]3. holding section

[0030]4. plate

[0031]5. cut

[0032]6. margin

[0033]7. multiple-stage press

[0034]8. component

[0035]9. first processing section

[0036]10. second processing section

[0037]11. third processing section

1. Method of fabricating pressed components from sheet steel that can beheat treated while inside the press, whereby the material is heated toabove its transformation point AC₃, pressed, and cooled, controlled, tobelow its crystalline-transformation point, characterized in that thesheet (1) is unwound from a coil, heated to above its transformationpoint, pressed in a press, and separated.
 2. Method as in claim 1,wherein the component is heated in a continuous furnace.
 3. Method as inclaim 1, wherein the component is heated inductively.
 4. Method as inclaim 3, wherein the component is inductively heated by transverse-fieldheating.
 5. Method as in claim 1, wherein the component is inductivelyheated to a preliminary temperature in two steps and then to its finaltemperature in a continuous furnace.
 6. Method as in claim 1,characterized in that the component is separated in two steps, whereby,in the first step, prior to being pressed, connections are left betweenthe component and the coil and, in the second step, subsequent to beingpressed, the component is completely separated.
 7. Method as in 6,wherein the first step of separation is carried out before the componenthas been heated.
 8. Method as in claim 1 characterized in that at leastone separation is carried out with a laser.
 9. Method as in claim 1,characterized in that the component is cooled in two steps, whereby, inthe first step, it is cooled to below the material's crystallinetransformation point and, in the second step, it is cooled toapproximately 50° C.
 10. Method as in claim 9, wherein the cooling thatoccurs during the second step is controlled.
 11. Method as in claim 1,characterized in that the starting material is coated steel sheet. 12.Method as in claim 1 characterized in that the starting material isuncoated steel sheet subjected to an inert atmosphere at least beforebeing exposed to heat prior to pressing.